Interpretive Summary: Crop rotation has been an important component of agricultural systems for centuries. With the advent of synthetic pesticides and fertilizers in the mid-20th century, however, extensive crop rotations were supplanted by intensive monoculture or short rotation cropping in many areas of the US. Concerns and costs associated with these intensely-managed systems include decreased soil organic matter, degraded soil structure, increased soil erosion, increased surface and groundwater contamination, and increased production costs. Research conducted previously at the Eastern South Dakota Soil and Water Research Farm has demonstrated that mineral nutrient accumulation and grain yield were greater in corn grown under annual rotation with soybean than in corn grown in monoculture. We were interested in determining whether a corn-soybean-wheat/alfalfa-alfalfa rotation would have similar beneficial effects on soil fertility and crop mineral nutrition. Our experimental objectives were to investigate the effects of complex crop rotation on soil fertility and corn mineral nutrient composition. Our data suggest that under the complex corn-soybean-wheat/alfalfa-alfalfa rotation, where maize followed a forage legume, maize grain yield was stable across all N input levels studied. Conversely, maize yield decreased as N input level was reduced under the C-C and C-S rotation treatments. Given the above-listed detrimental effects of monoculture or short rotation on natural resources and production efficiency, in conjunction with the findings of our study, it appears that substitution of complex crop rotation for N inputs may be an environmentally and economically sustainable practice.

Technical Abstract:
Yield of maize (Zea mays L.) rotated annually with soybean (Glycine max merr.) is better than its yield in monoculture. To determine how maize would respond to rotations that includes wheat (Triticum aestivum L.) and alfalfa (Medicago sativa L.) under different levels of N input, we evaluated N fertilizer input (8.5 or 5.3 Mg/ha yield goal, or no N) and crop rotation [C-C, continuous maize; C-S, maize-soybean; C-S-W/A-A, maize-soybean-wheat/alfalfa-alfalfa)] treatment effects on soil minerals, maize shoot dry weight and minerals (N, P, K, S, Ca, Mg, Fe, Mn, and Zn), grain yield, and grain composition (oil, starch, and minerals). Soil (0-30 cm depth) under the C-S-W/A-A rotation had greater NO3-N and less extractable P than the other rotations. Significant input x rotation interactions revealed that shoot concentrations of N, Ca, and Mg were less while P, K, and Zn were greater in the no N input/C-C treatment than other N input/rotation treatments. Discriminant analysis indicated that soil N, P, Ca, Zn, plant N, Zn, and grain N and S were important in differentiating between N input treatments. Soil N, grain N, S, P, Zn, and plant Ca were most important in differentiating between crop rotation treatments. No N input resulted in smaller yield and kernel N concentration within the C-C and C-S rotations but not C-S-W/A-A. Substitution of complex crop rotation for N inputs resulted in few differences in maize shoot and grain mineral relations and no yield reduction.